1. Field of the Invention (Technical Field)
The present invention relates to cameras and more particularly to controlling the viewing direction such as pan and tilt angles, of a camera with extreme weight, size, and power restrictions.
2. Background Art
The present invention solves the problem where a pan-tilt mechanism must be extremely light and small, because it is intended for a very small unmanned air vehicle (UAV). It must also consume little electrical power to maximize battery life. Presently, pan-tilt units for cameras are known standard devices that one can purchase. However, these units are large, heavy and consume significant electrical power. Conventional pan-tilt units for cameras rotate the camera and its lens using motors and gears and aim it in the desired direction as shown in FIG. 1. Camera 100 is rotated in pan direction 102 by gears or other well known method and in tilt direction 104 in a similar fashion to point camera lens 106 towards the desired direction. An example of this type of device, intended for UAV applications, can be found in an advertisement for devices sold by L3 Communications BAI Aerosystems on their netsite: http://www.bai.aero/payloads.html#series66. A system is needed to accomplish the same functionality with a system that is small, light and consumes only a fraction of the power required for the prior art systems. Further, a similar system is needed for use of infrared (IR) cameras and their lenses which are larger and heavier than conventional visual light cameras, making the prior art systems prohibitive for IR camera use in small UAVs.
Various optical systems, such as scanners and laser range finders, use mirrors to deflect laser beams. In addition, single lens reflex (SLR) cameras use mirrors to deflect images.
SLR cameras have been around for decades as shown in U.S. Pat. Nos. 6,390,692 and 5,715,003. These cameras use a mirror that deflects the image (that already passed the lens) into the viewfinder. When a picture is taken, the mirror flips up and the image can reach the film that is in the back of the camera. This assures that the photographer sees in the viewfinder exactly what the film will see, even if he changes the lenses between shots. These two prior art patents deal with improving the mirror mechanisms for SLR cameras.
U.S. Pat. No. 6,678,395 teaches a method of scanning an area with a mirror. The patent deals primarily with algorithms and methods that process data from a multi-spectral camera so as to detect targets with unique spectral and spatial characteristics. They use a gimbaled mirror to scan areas that are not directly under the rescue aircraft. They describe this feature as ‘the target area is scanned by a mirror oscillating about a scan axis across the flight path of the aircraft (cross-track)’. This prior art patent also discloses using the gimbaled mirror to deflect IR illumination at the area that is being captured by the camera. Yet another use of their gimbaled mirror is to stabilize the image by moving the mirror so as to offset aircraft vibrations. This device, in using a single mirror, cannot provide the coverage of the viewing area as the present invention. The present invention provides three hundred and sixty degree (360°) pan motion, preferably a plus or minus twenty-degree (±20°) tilt motion and capability to look down. The arrangement of mirrors and their rotations in the present invention meet all these specifications.
Another prior art patent is U.S. Pat. No. 6,396,233, which deals with a mirror-based gimbal for a target-tracking seeker for a missile. This is a device that is mounted in the nose of a missile and can point at targets that are not exactly along the longitudinal axis of symmetry of the missile. The scanning range of a seeker can be up to a ninety-degree (90°) cone, meaning that the seeker must be able to deflect plus or minus forty five-degrees (±45°) in all directions. Traditionally, in non-mirror-based designs, these motions are provided by two motors, one scanning left and right forty five-degrees (45°), and the other scanning up and down forty five-degrees (45°). This prior art patent replaces the two-motor design with a mirror suspended on a ball joint, which allows any angular rotation about the joint. This rotational freedom is controlled by four Kevlar lines pulled by computer-controlled capstans. For any angular position of the mirror, there is a set of lengths of the four lines that bring the mirror to that angular position. This prior art device suffers from the same deficiencies of the '395 patent in its limited viewing coverage.
The present invention is a method and apparatus that uses three light and small mirrors that can be rotated in such a way that they provide the desired viewing coverage and meet the weight and size constraints of a small UAV.